The present invention relates to retraction mechanisms for emergency locking safety belt retractors and more specifically to retraction mechanisms capable of selectively applying either of two different magnitudes of reel rewind bias to the safety belt retractor reel in response to rotational movement of the reel normally encountered during use of safety belt and harness straps employed with such retractors for holding vehicle occupants in their seats during emergency conditions.
Various types of dual tension safety belt retractor mechanisms have been employed heretofore for selectively applying a main spring rewind bias to the safety belt reel during normal belt protraction and retraction relative to the retractor and for applying a lower tension to the belt while the seat belt is in use about a vehicle occupant user.
As is presently known, it is desirable to reduce the tension in a chest belt of a safety harness for automotive passenger restraint when the belt is in use with an emergency locking type of retractor wherein the belt is prevented from protraction, reel unwinding movement, only when an emergency condition occurs. Since the belt is not prevented from an unwinding movement during normal wearing conditions, it is preferred that a rewind bias be continuously applied to the retractor reel in order to prevent buildup of slackness in the safety belt relative to the vehicle occupant employing such safety belt. Moreover, as is also known in the art, it is preferred that when the belt is in use, such rewind bias to prevent slackness in the belt be of a lower value than that normally applied for rewinding the belt onto the retractor reel when the belt is taken out of use.
An inherent feature of prior art dual tension safety belt retractors is the provision for reapplying the main spring bias to the safety belt reel when the belt is being used in the low tension biased mode and retraction of the belt is desired. Exemplary of such prior art dual tension retraction mechanisms are those disclosed in U.S. Pat. No. 4,165,844 issued to Akira Tanaka on Aug. 28, 1979. In the Tanaka patent, the main rewind spring is blocked out or locked to the retractor housing when the belt is in use (low tension mode). The unblocking or unlocking of the main spring for power retraction of the belt is accomplished by a partial rewinding of the belt reel under the low tension bias. This preliminary low tension rewinding which is necessary for reapplication of the main spring rewind bias is not always desirable. In many instances, for example when exiting a vehicle, it may be desirable to apply main spring rewind bias to the safety belt reel immediately without the necessity of a slow or occupant assisted initial rewind movement. Further, in this type of dual tension safety belt retractor mechanism, the degree to which the low tension bias may be lowered to ensure occupant comfort is limited since sufficient low tension bias must be maintained to allow positive retraction of the safety belt and buckle to ensure adequate rewind rotation to actuate the main spring rewind bias.
While the above discussed version of a dual tension retractor is believed to be commercially practicable and a satisfactory solution to a dual tensioning mechanism for emergency locking safety belt retractors, it has been recognized that it would be desirable to design a retractor having an externally operable release for applying main spring rewind bias to the safety belt for retraction without the necessity of an initial partial low tension biased belt retraction.